1. Field of the Invention
The present invention relates to a timing device for positioning a machine part which is moved by an actuator and a control circuit in a straight or circular path inside a housing. A timing decive, such as a disk or a timing ruler is used as a reference point for positioning, wherein the timing disk or timing ruler is arranged in a beam path of a light source-receiver unit (LRU).
2. Description of the Related Art
Timing devices of the aforedescribed type are disclosed, for example, in U.S. Pat. No. 5,859,425 (Ruhlatec Industrieprodukte GmbH). With such devices, the light of the radiation source must exit absolutely parallel so as to eliminate parallax errors when the light passes through the timing disk or the timing ruler. The lens systems used for this purpose are complex and quite expensive, but also have the disadvantage of increasing the overall length of the positioning device. Moreover, the optical correction device also has to be accurately positioned which is frequently quite difficult due to the differing designs.
It is therefore an object of the present invention to develop a device for positioning machine parts that move on a straight or circular path which uses a light source-receiver unit, wherein the light source-receiver unit operates with light sources of arbitrary design while still producing light beams with sufficient parallelism without requiring complex optical correction devices while simultaneously decreasing the overall length along the optical axis. The solution is based on a mask in the form of a film segment, wherein the mask is accurately positioned in the beam path of a light source-receiver unit by segregating and correlating the following functions:
The dimensions in two directions are correlated by the mask and the mask carrier (FIG. 3) and by the mask (FIG. 5), respectively, e.g., alignment in the film plane (2 axes). The third direction is defined through the attachment (e.g., with an adhesive) of the mask on the base plate. The base plate also provides the stability of the system.
The correlation of the dimensions of the mask with those of the timing disk is provided by spacer elements, (e.g., embossed spacers, such as projections or ribs) on the mask carrier (FIG. 4a) and on the base plate (FIG. 6), respectively.